What does ddclient do?

This tells changeip.com when my address changes. 

Why did I set up an account with change ip.com? 

I set up an account with change ip because it get an address for my computer that stays the same when ip address changes. 

What is an IP address?

An IP adress is physical location of my  computers connection to the internet. It changes when I connect with a different net work.Sometimes a network shares one ip address with more than one device. In that each device gets an internal network address. Most networks such as bright house gives you one IP address so your router  must give each device its own internal address. The network has to map port numbers to the from the public ip address to the internal IP addresses.  

What is a port number?

Aport number is the number of a service running on your computer that listens for traffic. The port number on your computer tells them which traffic os addressed to them. For example port 80 and 443 address traffic to the web server.

How did we get ddclient working?

We installed it on my Mac using Homebrew. the command is

brew install ddclient

Homebrew gives instructions when it installs ddclient for creating a configuration file with an example. The example has a section for changeip.com. We fallowed the example and had to add an extra line at the beginning to get it working.

use=web, web=ip.changeip.com:8245